We find evidence for a bimodal distribution of small planet sizes. Sub-Neptunes and super-Earths appear to be two distinct planet classes. Planets tend to prefer radii of either ∼1.3 R⊕ or ∼2.4 R⊕, with relatively few planets having radii of 1.5–2.0 R⊕.

And now, a team of international astronomers has announced the discovery of an extra-solar body that is similar to another terrestrial planet in our own Solar System. It’s known as Kepler-1649b, a planet that appears to be similar in size and density to Earth and is located in a star system just 219 light-years away. But in terms of its atmosphere, this planet appears to be decidedly more “Venus-like” (i.e. insanely hot!)

The team’s study, titled “Kepler-1649b: An Exo-Venus in the Solar Neighborhood“, was recently published in The Astronomical Journal. Led by Isabel Angelo – of the SETI Institute, NASA Ames Research Center, and UC Berkley – the team included researchers also from SETI and Ames, as well as the NASA Exoplanet Science Institute (NExScl), the Exoplanet Research Institute (iREx), the Center for Astrophysics Research, and other research institutions.

Astronomers have detected an atmosphere around the super-Earth GJ 1132b. This marks the first detection of an atmosphere around a low-mass super-Earth, in terms of radius and mass the most Earth-like planet around which an atmosphere has yet been detected. Thus, this is a significant step on the path towards the detection of life on an exoplanet. The team, which includes researchers from the Max Planck Institute for Astronomy, used the 2.2-m ESO/MPG telescope in Chile to take images of the planet's host star, GJ 1132, and measured the slight decrease in brightness as the planet and its atmosphere absorbed some of the starlight while passing directly in front of their host star.

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The team used the GROND imager at the 2.2-m ESO/MPG telescope of the European Southern Observatory in Chile to observe the planet simultaneously in seven different wavelength bands. GJ 1132b is a transiting planet: From the perspective of an observer on Earth, it passes directly in front of its star every 1.6 days, blocking some of the star's light.

The size of stars like GJ 1132 is well known from stellar models. From the fraction of starlight blocked by the planet, astronomers can deduce the planet's size—in this case around 1.4 times the size of the Earth. Crucially, the new observations showed the planet to be larger at one of the infrared wavelengths than at the others. This suggests the presence of an atmosphere that is opaque to this specific infrared light (making the planet appear larger) but transparent at all the others. Different possible versions of the atmosphere were then simulated by team members at the University of Cambridge and the Max Planck Institute for Astronomy. According to those models, an atmosphere rich in water and methane would explain the observations very well.

The discovery comes with the usual exoplanet caveats: while somewhat larger than Earth, and with 1.6 times Earth's mass (as determined by earlier measurements), observations to date do not provide sufficient data to decide how similar or dissimilar GJ 1132b is to Earth. Possibilities include a "water world" with an atmosphere of hot steam.

The presence of the atmosphere is a reason for cautious optimism. M dwarfs are the most common types of star, and show high levels of activity; for some set-ups, this activity (in the shape of flares and particle streams) can be expected to blow away nearby planets' atmospheres. GJ 1132b provides a hopeful counterexample of an atmosphere that has endured for billion of years (that is, long enough for us to detect it). Given the great number of M dwarf stars, such atmospheres could mean that the preconditions for life are quite common in the universe.

In any case, the new observations make GJ 1132b a high-priority target for further study by instruments such as the Hubble Space Telescope, ESO's Very Large Telescope, and the James Webb Space Telescope slated for launch in 2018.

Interesting 3:2 orbital resonances between planets b and c, c and d, and d and e.

A very interesting compact system around a late G dwarf, which makes these planets *hot*. Sadly, no observed TTVs so it will be a while before we know mass/density.

Worth noting this was from the Campaign 12 raw cadence data (the processed data has not yet been released to MAST). I'm hoping this sets a precedent for future campaigns :-)

This weekend, I'll try and produce a light curve for this one (but my raw cadence code still needs a fair bit of debug).

There are quite a few new candidates from this Exoplanet Explorers search, some in earlier quarters, so once again, the human eyeball has found things missed by the automated pipelines. Clearly some will be false positives (BGEB contamination is most likely).

Edit: taking much longer than expected as the MAST download of the raw cadence data is glacial.

The newly detected TRAPPIST-1 system, with seven low-mass, roughly Earth-sized planets transiting a nearby ultra-cool dwarf, is one of the most important exoplanet discoveries to date. The short baseline of the available discovery observations, however, means that the planetary masses (obtained through measurement of transit timing variations of the planets of the system) are not yet well constrained. The masses reported in the discovery paper were derived using a combination of photometric timing measurements obtained from the ground and from the Spitzer spacecraft, and have uncertainties ranging from 30\% to nearly 100\%, with the mass of the outermost, P=18.8d, planet h remaining unmeasured. Here, we present an analysis that supplements the timing measurements of the discovery paper with 73.6 days of photometry obtained by the K2 Mission. Our analysis refines the orbital parameters for all of the planets in the system. We substantially improve the upper bounds on eccentricity for inner six planets (finding e<0.02 for inner six known members of the system), and we derive masses of 0.79±0.27M⊕, 1.63±0.63M⊕, 0.33±0.15M⊕, 0.24+0.56−0.24M⊕, 0.36±0.12M⊕, 0.566±0.038M⊕, and 0.086±0.084M⊕ for planets b, c, d, e, f, g, and h, respectively.

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Figure 4 indicates that – to within the errors of our determinations – the four most distant planets are consistent with pure water compositions, and in any event, are substantially less dense either Mars or Venus.

The newly detected TRAPPIST-1 system, with seven low-mass, roughly Earth-sized planets transiting a nearby ultra-cool dwarf, is one of the most important exoplanet discoveries to date. The short baseline of the available discovery observations, however, means that the planetary masses (obtained through measurement of transit timing variations of the planets of the system) are not yet well constrained. The masses reported in the discovery paper were derived using a combination of photometric timing measurements obtained from the ground and from the Spitzer spacecraft, and have uncertainties ranging from 30\% to nearly 100\%, with the mass of the outermost, P=18.8d, planet h remaining unmeasured. Here, we present an analysis that supplements the timing measurements of the discovery paper with 73.6 days of photometry obtained by the K2 Mission. Our analysis refines the orbital parameters for all of the planets in the system. We substantially improve the upper bounds on eccentricity for inner six planets (finding e<0.02 for inner six known members of the system), and we derive masses of 0.79±0.27M⊕, 1.63±0.63M⊕, 0.33±0.15M⊕, 0.24+0.56−0.24M⊕, 0.36±0.12M⊕, 0.566±0.038M⊕, and 0.086±0.084M⊕ for planets b, c, d, e, f, g, and h, respectively.

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Figure 4 indicates that – to within the errors of our determinations – the four most distant planets are consistent with pure water compositions, and in any event, are substantially less dense either Mars or Venus.

It is quite remarkable that the density drops significantly below the 3-5 range (= Earth-like, rocky planets) for the planets with equilibrium temperatures below 0°C, the freezing point of water (at 1 bar, but its quite possible that these planets have ~1 bar atmospheres). This might suggest the outer planets f,g,h are essentially super-Ganymedes.

An exoplanet orbiting a red dwarf star 40 light-years from Earth may be the new holder of the title “best place to look for signs of life beyond the Solar System”. Using ESO’s HARPS instrument at La Silla, and other telescopes around the world, an international team of astronomers discovered a “super-Earth” orbiting in the habitable zone around the faint star LHS 1140. This world is a little larger and much more massive than the Earth and has likely retained most of its atmosphere. This, along with the fact that it passes in front of its parent star as it orbits, makes it one of the most exciting future targets for atmospheric studies. The results will appear in the 20 April 2017 issue of the journal Nature.

The newly discovered super-Earth LHS 1140b orbits in the habitable zone around a faint red dwarf star, named LHS 1140, in the constellation of Cetus (The Sea Monster) [1]. Red dwarfs are much smaller and cooler than the Sun and, although LHS 1140b is ten times closer to its star than the Earth is to the Sun, it only receives about half as much sunlight from its star as the Earth and lies in the middle of the habitable zone. The orbit is seen almost edge-on from Earth and as the exoplanet passes in front of the star once per orbit it blocks a little of its light every 25 days.

“This is the most exciting exoplanet I’ve seen in the past decade,” said lead author Jason Dittmann of the Harvard-Smithsonian Center for Astrophysics (Cambridge, USA). “We could hardly hope for a better target to perform one of the biggest quests in science — searching for evidence of life beyond Earth.”

"The present conditions of the red dwarf are particularly favourable — LHS 1140 spins more slowly and emits less high-energy radiation than other similar low-mass stars," explains team member Nicola Astudillo-Defru from Geneva Observatory, Switzerland [2].

For life as we know it to exist, a planet must have liquid surface water and retain an atmosphere. When red dwarf stars are young, they are known to emit radiation that can be damaging for the atmospheres of the planets that orbit them. In this case, the planet's large size means that a magma ocean could have existed on its surface for millions of years. This seething ocean of lava could feed steam into the atmosphere long after the star has calmed to its current, steady glow, replenishing the planet with water.

The discovery was initially made with the MEarth facility, which detected the first telltale, characteristic dips in light as the exoplanet passed in front of the star. ESO’s HARPS instrument, the High Accuracy Radial velocity Planet Searcher, then made crucial follow-up observations which confirmed the presence of the super-Earth. HARPS also helped pin down the orbital period and allowed the exoplanet’s mass and density to be deduced [3].

The astronomers estimate the age of the planet to be at least five billion years. They also deduced that it has a diameter 1.4 times larger than the Earth — almost 18 000 kilometres. But with a mass around seven times greater than the Earth, and hence a much higher density, it implies that the exoplanet is probably made of rock with a dense iron core.

This super-Earth may be the best candidate yet for future observations to study and characterise its atmosphere, if one exists. Two of the European members of the team, Xavier Delfosse and Xavier Bonfils both at the CNRS and IPAG in Grenoble, France, conclude: “The LHS 1140 system might prove to be an even more important target for the future characterisation of planets in the habitable zone than Proxima b or TRAPPIST-1. This has been a remarkable year for exoplanet discoveries!” [4,5].

In particular, observations coming up soon with the NASA/ESA Hubble Space Telescope will be able to assess exactly how much high-energy radiation is showered upon LHS 1140b, so that its capacity to support life can be further constrained.

Further into the future — when new telescopes like ESO’s Extremely Large Telescope are operating — it is likely that we will be able to make detailed observations of the atmospheres of exoplanets, and LHS 1140b is an exceptional candidate for such studies.

What to make of Fergus Simpson’s new paper on waterworlds, suggesting that most habitable zone planets are of this type? If such worlds are common, we may find that most planets in the habitable zones of their stars are capable of evolving life, but unlikely to host technological civilizations. An explanation for the so-called ‘Fermi Paradox’? Possibly, but there are all kinds of things that could account for our inability to see other civilizations, most of them covered by Stephen Webb in his If the Universe Is Teeming with Aliens … Where Is Everybody? (2nd ed., Springer 2015), which offers 75 solutions to the problem.

Simpson (University of Barcelona) makes his case in the pages of Monthly Notices of the Royal Astronomical Society, arguing that the balance maintained by a planetary surface with large amounts of both land and water is delicate. The author’s Bayesian statistical analysis suggests that most planets are dominated either by water or land, most likely water. Earth may, then, be something of an outlier, with most planets over 90 percent covered in water.

There seems to be a confusion in terminology prevalent. Is a waterworld a world covered in water, but which, like the Earth, is predominately made of rock and metal; or is a waterworld one which is predominately made of water (ice, actually)?

I think of a waterworld as being the latter, with the former described as an oceanworld. But I could be under a misapprehension!

There seems to be a confusion in terminology prevalent. Is a waterworld a world covered in water, but which, like the Earth, is predominately made of rock and metal; or is a waterworld one which is predominately made of water (ice, actually)?

I think of a waterworld as being the latter, with the former described as an oceanworld. But I could be under a misapprehension!

I think of it as a watery Earth myself as that seemed to be what the article was referencing.

Small planets may be common around ultracool dwarfs, an idea that previous microlensing discoveries reinforce, along with the work on protoplanetary disks and the seven planets orbiting TRAPPIST-1. As to our expectations regarding planets in the galactic bulge as opposed to the disk, the jury is still out. The planets Spitzer has thus far found in its microlensing campaign for the galactic distribution of planets are all located in the disk. We have two upcoming Spitzer microlensing campaigns, one this year and one next, which should offer additional insights. The key question: Is the galactic bulge deficient in planets?

If & when a future ultra-sensitive spectroscope detects chlorophyll in an exoplanet's atmosphere -- meaning ongoing photosynthesis by abundant plant life -- will NASA (plus maybe other government's space agencies) mount a hugely expensive effort (hundreds of billions of dollars) to send a robotic probe to that planet over a distance of, say, 20 lightyears? Knowing that radio transmission of results won't be received by anyone currently living? And with no guarantee of success?

Yes: Explore & investigate is in our genes, must find out if this is a Second Earth that can be our lifeboat & refuge

"(hundreds of billions of dollars) to send a robotic probe to that planet over a distance of, say, 20 lightyears" - well, such a probe could reach its destination somewhere in the year 50000, at best. Does not make sense, if you ask me...

"(hundreds of billions of dollars) to send a robotic probe to that planet over a distance of, say, 20 lightyears" - well, such a probe could reach its destination somewhere in the year 50000, at best. Does not make sense, if you ask me...

If & when a future ultra-sensitive spectroscope detects chlorophyll in an exoplanet's atmosphere -- meaning ongoing photosynthesis by abundant plant life -- will NASA (plus maybe other government's space agencies) mount a hugely expensive effort (hundreds of billions of dollars) to send a robotic probe to that planet over a distance of, say, 20 lightyears? Knowing that radio transmission of results won't be received by anyone currently living? And with no guarantee of success?

Yes: Explore & investigate is in our genes, must find out if this is a Second Earth that can be our lifeboat & refuge

No: We will never leave solar system, age of discovery is over

I'll echo that: Is it a trick question?

Some of the problems: - Science & technology & societal development is not decided by polls.- Finding biotic signatures is discovery. The (non)question is how fast this age of discovery will put up larger observatories to find out more. My guess: very quickly.

The lifeboat/refuge/faster probes perspective is Utopia fantasy, as far as I can see. [Admittedly: 1. I am tired of seeing such ideas around discussions containing a smidgen of science. The at odds juxtaposition is like scratching sounds from a window. But never mind that. 2. Something like Starshot may be feasible and complement other methods of discovery. Scaled up such can carry spores or even seeds, but not implant anything like our biosphere - such evolution will end up somewhere else in phylogenetic tree space. It would be a possible life refugia at best. But life is likely common, seeing how fast it emerged on Earth.]

Relativity physics puts a hard limit on economical expansion or 'refuge' (if not refugia) ideas. Whether or not individuals or even worlds would - like any parent - put aside resources for direct colonization is an open question.

[But I am reminded of the xkcd comic where Randall shows that on an exponential scale - the scale of economical growth - colonizing the Oort cloud is the largest effort after the Moon. From the Oort cloud the distance to the next cloud is nothing in relation. So if and when we colonize the resource full innards of Oort objects and put rocket engines on the outside - because orbiting is such a bounded life - I expect we will seed the galaxy. My guess: it will happen. But I do not see any connection with fears of extinction.]

Here is the crucial point as far as I can see: our species will go extinct. Nothing can or should stop that anymore than we can or should stop the death of individuals, assuming we want to continue evolving in order for the process of life to continue. The average lifetime of a mammal species is 1-2 Myrs, and we can see from H. erectus that the Homo lineage is, despite the bushy behavior, no exception. Even colonization won't stop that since speciation is an incipient process as soon as population interbreeding drops under an average of 1 breeding/generation. [A somewhat curious result from population genetics, the population sizes are divided out of the problem.]

Life on the other hand may never go extinct as long as it finds a habitable environment. Our one sample is roughly as old as the habitable environment on Earth, indicating a mature biosphere is hardy. I expect our soon-to-come - give or take a Myr - descendants will remember us fondly in the way we remember our great grandparents. "But they lived then, we live now."